River Ice BreakupRiver Ice Breakup

Introductory lectures in

River Ice EngineeringIntroductory lectures in

River Ice Engineering

photo by S. Beltaosphoto by S. Beltaos

ThermalThermal versus versus DynamicDynamic Breakup Breakup

• Breakup is influenced by both thermal Breakup is influenced by both thermal (meteorological) and dynamic (hydraulic) (meteorological) and dynamic (hydraulic) processes.processes.

• It is the relative importance of these It is the relative importance of these interacting influences which dictate the interacting influences which dictate the nature and severity of river ice breakup.nature and severity of river ice breakup.

Thermal BreakupThermal Breakup

• Ice deterioration occurs much as it does Ice deterioration occurs much as it does in a lake – ice simply “rots” in placein a lake – ice simply “rots” in place

• Meteorological factors are most Meteorological factors are most important – energy budget calculationimportant – energy budget calculation

• Hydraulic influences are negligibleHydraulic influences are negligible

Important Meterological FactorsImportant Meterological Factors

• Solar insolation and warm overlying airSolar insolation and warm overlying air

• Reflectance (“albedo”) of the surfaceReflectance (“albedo”) of the surface

• fresh snow: albedo ~ 0.90 to 0.95fresh snow: albedo ~ 0.90 to 0.95

• open water: albedo ~ 0.05 to 0.15open water: albedo ~ 0.05 to 0.15

ThermalThermal Breakup Processes Breakup Processes

1. snowmelt – reduces surface albedo

photo by F. Hicksphoto by F. Hicks

ThermalThermal Breakup Processes Breakup Processes

2. development of open water leads – allow considerable heat to enter the flow, melting the ice from the underside

photo by F. Hicksphoto by F. Hicks

ThermalThermal Breakup Processes Breakup Processes3. thermal deterioration of the ice cover – occurs at an

accelerating rate, as surface albedo decreases

photo by S. Beltaos

DynamicDynamic Breakup Breakup

• Breakup is strongly influenced by dynamic Breakup is strongly influenced by dynamic (hydraulic) factors – usually associated with a large (hydraulic) factors – usually associated with a large snowmelt runoff event.snowmelt runoff event.

• Before any significant thermal deterioration has Before any significant thermal deterioration has occurred, the ice cover is lifted by rapidly increasing occurred, the ice cover is lifted by rapidly increasing water levels and it breaks into discrete pieces.water levels and it breaks into discrete pieces.

• Ice sheets and ice floes will be carried downstream Ice sheets and ice floes will be carried downstream with the flood flow.with the flood flow.

• An ice jam will form if the ice run is arrested.An ice jam will form if the ice run is arrested.

DynamicDynamic Breakup Processes Breakup Processes

1. overflow from open 1. overflow from open leads – indication of leads – indication of rapid water level riserapid water level rise

photos by F. Hicksphotos by F. Hicks

2. Formation of Hinge Cracks

a)a) As streamflow increases due to spring runoff, the ice cover in As streamflow increases due to spring runoff, the ice cover in the centre portion of the channel will lift.the centre portion of the channel will lift.

b)b) Hinge cracks form parallel to the banks.Hinge cracks form parallel to the banks.

c)c) Border ice becomes inundated.Border ice becomes inundated.

(Beltaos, 1995)(Beltaos, 1995)

Hinge Crack in a Narrow Stream

Typically, hinge cracks Typically, hinge cracks form along both banks, form along both banks, but in narrow channels, but in narrow channels, like this one, a single like this one, a single crack may form down crack may form down the middle of the the middle of the channel.channel.

Notice the water on top Notice the water on top of the ice on either side of the ice on either side of the crack.of the crack.

photo by S. Beltaosphoto by S. Beltaos

3. Transverse cracking3. Transverse cracking

As the ice cover lifts with the rising water level, transverse cracks form.

photo by S. Beltaosphoto by S. Beltaos

Transverse cracking

Border ice inundation

photo by S. Beltaos

4. Ice Clearing4. Ice ClearingWhen the discharge gets high enough for the lifting ice sheets When the discharge gets high enough for the lifting ice sheets to be able to overcome geometric constraints, these sheets are to be able to overcome geometric constraints, these sheets are then free to pass downstream.then free to pass downstream.

(Beltaos, 1995)(Beltaos, 1995)

DynamicDynamic Breakup Processes Breakup Processes

4. Ice Clearing4. Ice Clearing

photo by S. Beltaos

DynamicDynamic Breakup Processes Breakup Processes

5. ice run5. ice run

6. ice jamming6. ice jamming

photo by F. Hicksphoto by F. Hicks

photo by R. Gerard

Ice Jams form when dynamic processes dominateIce Jams form when dynamic processes dominate

photo by L. Garner

Flooding usually results…Flooding usually results…

photo by S. Beltaos

ice jam near Fredericton, NB…ice jam near Fredericton, NB…

photo by D. Bray

Profile of a Long Ice JamProfile of a Long Ice Jam

Toe of Jam

Head of JamBackwater

(adapted from Ashton, 1986)(adapted from Ashton, 1986)

Ice jams can be a big problem for bridges…Ice jams can be a big problem for bridges…

photo source: R. Gerard

Ice jams are often too big to remove …Ice jams are often too big to remove …

Blasting is usually ineffective in such cases.CRREL photo

jam toe was herejam toe was here

Large trees on this island were “mowed down” by an ice jam…Large trees on this island were “mowed down” by an ice jam…

photo by R. Gerard

(Allen, 1977)

Mean ice free data on rivers